The present disclosure relates generally to facsimile transmission through communication networks, and more particularly to transmission via facsimile in a network with silence suppression.
Facsimile document transmission continues to have an important role in business communications for a number of reasons, including the ability to transfer images not stored on a local computer, legal acceptance of handwritten signatures, real-time confirmation of receipt, confidence in what has been received, and the ability to provide a ‘tamper resistant’ copy of the information transferred. The ubiquitous nature of facsimile machines on a global scale allows them to easily take advantage of existent telecommunications networks. Facsimile machines may also be shared by a number of individuals so that sending and receiving documents can be relatively efficient among a general population or group of persons.
While facsimile communications have previously been implemented over circuit switched networks, such as the publicly switched telephone network (PSTN), packet switched networks, such as IP networks, have been implemented to carry communications including facsimile communications. Because circuit switched networks enjoyed wide use throughout the world, and packet switched networks have been introduced relatively recently, translation and communication between different types of networks has become an important part of communications, including facsimile communications.
Translation between circuit switched and packet switched communication networks typically involves the use of translation between different protocols. Sometimes, protocols that might be desired for certain types of communications are not supported in all parts of a packet switched network, such as an IP network. For example, a facsimile transmission may be sent from a PSTN-based originator to a facsimile destination through an IP network using an IP media gateway. The facsimile communication is routed to an appropriate destination over the IP network in accordance with the facsimile communication parameters. However, some links in the IP network may not support a desired facsimile transmission protocol.
Referring to FIG. 1, a conventional communication network 100 that permits facsimile transmission is illustrated. In network 100, a facsimile device 110 or a facsimile device 124 may originate or receive a facsimile transmission through analog signalling. For example, facsimile device 110 may originate or receive a facsimile transmission that is sent over a Public Switched Telephone Network (PSTN) 112. Facsimile device 110 or 124 may operate using G3 (Group 3) type facsimile transmissions according to facsimile protocols such as the V.17, V.21, V.27 or V.29 facsimile protocols. Facsimile device 110 or 124 may operate using SG3 (Super Group 3) type facsimile transmissions according to the V.34 facsimile protocol. G3 and SG3 type facsimile communications conform to the ITU (International Telecommunication Union) Recommendation T.30 for facsimile transmission in the general switched telephone network, as may be implemented with network 100. PSTN 112 in network 100 may operate with communication protocols for a circuit switched network, such as SS7, T1, E1 and other circuit switched signalling and data communication protocols.
PSTN 112 is connected to an IP Media Gateway 114, which can perform translations between PSTN 112 and protocols used in an IP network 116. IP network 116 is a packet switched network that may implement the Internet Protocol (IP) routing and addressing methodology to transfer data packets. IP network 116 may implement various transport protocols, which may include UDP, TCP, RTP and other media and data communication protocols for packet switched networks. IP network 116 may be implemented to provide facsimile transmission support with facsimile transmission protocols such as the T.38 protocol for real time facsimile transmission. IP network 116 may include a number of nodes through which a facsimile transmission originating at facsimile device 110 may travel. A facsimile transmission or communication may be composed of facsimile setup or control commands, training data or image data, which may be referred to herein collectively as “facsimile messages.”
One or more of the nodes in IP network 116 may not support real time facsimile protocols such as the T.38 protocol. In such a case, IP network 116 relays the realtime facsimile messages using a facsimile passthrough technique that involves other types of protocols and codecs for handling facsimile transmissions originating from the PSTN 112. Currently, the most commonly used facsimile passthrough codecs are the G.711 (64 KBPS) and G.726 (32 KBPS) codecs, which are well suited for facsimile transmission due to the low compression levels involved in implementing the codecs. The low compression levels make it possible for facsimile modem data to be preserved through the compression process with sufficient integrity to permit successful facsimile transmission. The G.711 is currently the most frequently used to implement support for facsimile passthrough communications. The G.711 and G.726 codecs are low in complexity, so that they can be easily implemented, but are not bandwidth efficient relative to codecs that are optimized for voice communications, such as the G.729 codec. Accordingly, the G.711 and G.726 codecs are seldom currently used by carriers and service providers in a communication network to carry voice traffic because of their typically higher bandwidth usage.
The devices connected to IP network 116, such as IP facsimile device 118, IP facsimile server 120, analog telephone adapter 122, which can also serve as an IP Media Gateway, and IP Media Gateway 114 may implement various codecs and/or protocols to provide a variety of communication transmissions. For example, G3 that take advantage of voice activity detection (VAD) during voice calls to reduce network bandwidth utilization. Nodes or IP endpoints of IP network 116 that implement VAD operate by avoiding the transmission of non-speech segments of communications to permit reduced bandwidth usage. For example, during speech oriented telephone calls, the communications tend to be half-duplex in nature. In such a scenario, voice conversation transmissions can readily take advantage of VAD to reduce bandwidth usage that is used to carry voice data, and to avoid carrying communication transmissions that have silence for voice data. This type of silence suppression substitutes “silence” packets for non-speech packets to avoid sending packets that might amplify noise picked up during transmission. Thus, active voice conversations can be carried without also carrying non-speech data, which in turn permits a reduced bandwidth usage for voice conversation type communications to enable communication networks to operate more efficiently.
In the case of modem communications, including facsimile communications, silence suppression or VAD is generally disabled, since it is implemented typically for voice communications, and can have drawbacks for other types of communications, including facsimile communications. For example, silence suppression or VAD can contribute to signal clipping, which can negatively impact modem data being transported in the communication network. Facsimile passthrough calls typically do not use silence suppression or VAD to avoid corruption of facsimile data as a result of valid facsimile signals being suppressed when they are detected as noise instead of voice communications. Accordingly, facsimile passthrough communications in an IP network with nodes that may not support real time facsimile protocols, such as the T.38 protocol, typically consume more bandwidth than is necessary to complete the facsimile communications.